Research on human cytomegalovirus (CMV) is designed to develop an understanding of the regulation of a complicated DNA virus genome. This virus can replicate in cells of human origin or remain latent in these cells for extended periods of time. The problem is to be approached by characterizing the transcription of the CMV genome in permissive cells that permit viral DNA replication and infectious virus production and in nonpermissive cells that allow early viral gene expression but no viral DNA replication or detectable late gene expression. The nonpermissive cell is being used as an example of a cell that favors latency of the CMV genome. The origin of viral transcripts synthesized in permissive and nonpermissive cells will be mapped on the viral genome. Host- or virus-induced proteins that may be regulatory proteins because they influence viral gene transcription, bind to the viral DNA, covalently link to viral DNA, or interact with host cell chromatin will be characterized to understand the regulation of viral replication and the interaction of viral gene products with the host cell. I also propose to initiate in vitro mRNAs from defined regions of the viral genome. The organization of the CMV genome and its replication in permissive and nonpermissive cells will be related to the latent or persistent infectious potential of the virus in humans.